Github user mn-mikke commented on the issue:
https://github.com/apache/spark/pull/21687
@viirya Yeah, it looks like the same problem, but It's worked around via
different implementation of ```IfCoercion``` rule. This rule utilizes ```!=```
operator for comparison. So if two types differ in nullability flags, casting
is applied to get the types alligned.
```CaseWhenCoercion``` rule utilizes ```sameType``` instead. We could
change this rule according to the ```IfCoercion``` rule, but is it neccesary to
do that?
An extra ```Cast``` expression won't perform any effective casting (int to
int, string to string,...). We just need to supply correct meta-data
information to parent expressions to perform null-safe codegen.
Personally, I would resolve this nullability problem in expressions, not it
coercion rules. WDYT?
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